This invention relates to semiconductor material processing, and more particularly to methods for maintaining the physical shape of material islands while rearranging their crystalline structure.
The recent trend in digital equipment has been for faster operation, and more devices on less physical space. One thing that is basic to improve both of these criteria is better semiconductor material, both in terms of operating characteristics and yield. A recent development in material processing is to use laser annealing (Electronic Design, Jan. 18, 1979) to repair surface damage to semiconductor wafers. Damage to the wafer surface occurs during ion implantation in the form of crystal lattice breakdown, driving the surface to an amorphous noncrystalline state. Previous to the laser annealing, the only method for repair was to place the wafer in an oven at 1000.degree. C. and let the lattice structure reform (about two hours). This often caused undesirable shifts in implant profile. Laser annealing requires only about three minutes per wafer, and keeps implant profiles relatively the same, and gets almost perfect recrystallization and electrical activity of the surface. In instances where deposited islands of poly-silicon are to be annealed (Gibbons et al in Applied Physic Letters, Vol. 34, No. 12, June 15, 1979) it has been shown that the full depth of the island must be melted to achieve recrystallization in the desired manner. When the island material is melted by the laser, two problems are encountered. With no support, the edges of the island become rounded, and lose shape. Also, the surface tension of the material causes the surface to bead up, and as a result of the uneven surface, the material quality is degraded.
An object of the present invention is to provide physical support to the islands of semiconductor material to prevent edge rounding, and prevent beading on the surface.